replace string with string+new line in file

Question

Ongoing Series
Series 2
Series 1

I want to insert series 3 between first and second line with replacing series 2 with series 3 \\n series 2 using file_get_contents file_put_contents with out success

Answer 1

$text = file_get_contents("myfile.txt")
$text = preg_replace('/Series 2\s+/si', 'Series 2\nSeries 3\n', $text);
file_put_contents("newfile.txt", $text);

Answer 2

$flename = "filename";
$newString = "series 3"; 

// Read file to array
$lines = file($filename);
// Add line after the fist one 
array_splice($lines, 1, 0, $newString . PHP_EOL);
// Write back
file_put_contents($filename, implode('', $lines));